This invention relates to gear transmissions, and in particular it relates to an improved two-speed planetary gear transmission.
Many types of two-speed gear transmissions are known, such as for use with a hydrodynamic transmission, i.e. a torque converter, and these include planetary gear transmissions providing direct drive by using a clutch to operatively connect the input and output shafts for rotation together, and providing overdrive or underdrive by using a brake to hold one of the sun or ring gears stationary relative to a casing. However, such known two-speed gear transmissions include power shift friction couplings and are normally very heavy due to the high capacity of the clutch and the brake. If the transmission is simplified by the use of a free wheel instead of a power shift coupling, then of course the gear transmission cannot transmit torque in both directions, i.e. driving torque and braking torque. Moreover, the forces of the clutch or brake which are exerted upon rotary bearings of the two-speed gear transmission which are in motion have either resulted in short bearing life and/or have resulted in requiring a rather large design of the transmission so as to provide an overall structure and bearings which can withstand such clutch and brake forces.
Hence, there exists a need for providing a two-speed planetary gear transmission having improved clutch and brake force characteristics which will permit the design of a two-speed planetary gear transmission of the type described which is more compact and/or wherein the wear upon the bearings is reduced, and which can transmit torque in both directions, i.e. drive torque and braking torque, in both direct drive and overdrive or underdrive.